1. Field of the Invention
The present invention relates to an exposure method and an exposure system used for a lithography process in a fabrication of a semiconductor device and a recording medium storing a program for executing by a computer a process in the exposure method and the exposure system.
2. Description of the Related Art
A film pattern forming process has been often used in the fabrication of the semiconductor device and it is an important process that has a great influence on the performance of a semiconductor element. The film pattern forming process comprises the steps of: forming a conductive film, an insulating film and the like on a semiconductor substrate (semiconductor wafer); coating a photoresist (photosensitive organic resin) film on the formed film; forming a photomask pattern in the photoresist film by exposing a light onto the photoresist film via a photomask; developing the photomask pattern to form the photoresist pattern corresponding to the photomask pattern; and etching the above described conductive or insulating film with this photoresist pattern as a mask to form a film pattern (LSI pattern). A process is used, which is referred to as a photolithography process, wherein photoresist is coated on a semiconductor substrate, a mask pattern is baked on the coated photoresist and the baked mask pattern is developed to form a predetermined photoresist pattern. In an exposing step, a photomask is used. The photomask is a transparent substrate made of, for example, silica, and a mask pattern made of, for example, chrome is formed on the upper surface of the photomask. The photomask is required to have high accuracy in order to obtain a highly accurate photoresist pattern.
Before a fresh photomask is used to expose a wafer to light, it is tested for its optimum exposure conditions (optimum exposure condition detection), as described below.
Conventionally, an exposure for the optimum exposure condition detection has been conducted according to a procedure shown in a process flow of FIG. 12. Specifically, an exposure is conducted onto a sample wafer via the fresh photomask, while changing the chip areas (exposed areas) and also changing the exposure dosage and focus, to form the photomask pattern on the photoresist film coated on the sample wafer. The photomask pattern formed on the photoresist film is developed to form the resist pattern on each chip area (step Si). FIG. 13 is a plan view of the sample wafer, showing a large number of exposure areas (chip areas). After development, a line width of the acquired resist pattern is measured by a scanning electron microscope and the like (step S2). In general, the measurement result is as shown in FIG. 14. Based on the measurement result, the optimum exposure conditions, that is, the optimum exposure, the optimum focus and the like, are obtained (step S3). Based on the obtained optimum conditions, an exposure is conducted for the practical wafers (step S4). These operations are conducted every time a fresh mask is used.
However, the above described optimum exposure condition detection operation has a large number of steps and is so complicated that an operation efficiency is extremely lowered.
According to a first aspect of the present invention, there is provided an exposure method comprising exposing a light on a photomask having a mask pattern, in an exposing device; receiving in the exposing device the light which passed through the photomask to observe an optical image of the mask pattern based on the received light; deciding an optimum exposure condition based on the optical image of the mask pattern to form a predetermined resist pattern; and exposing a light on a photoresist film formed on a wafer via the photomask based on the optimum exposure condition.
According to a second aspect of the present invention, there is provided an exposure method comprising exposing a light on a photomask having a device pattern and a reference mark; receiving the light which passed through the photomask and observing an optical image of the reference mark based on the received light; inferring a dimension of the device pattern based on the observed optical image of the reference mark; deciding an optimum exposure condition for forming a predetermined resist pattern, based on the inferred dimension of the device pattern; and exposing a light on a photoresist film formed on a wafer via the photomask based on the optimum exposure condition.
According to a third aspect of the present invention, there is provided a system of exposing a light on a photomask having a mask pattern comprising an observing device in an exposure apparatus, which receives a light which passed through a photomask and observes an optical image of a mask pattern of the photomask based on the received light; a deciding device which decides an optimum exposure condition for forming a predetermined resist pattern, based on the optical image of the mask pattern; and an exposure apparatus which exposes a light on a photoresist film formed on a wafer via the photomask, based on the optimum exposure condition.
According to a fourth aspect of the present invention, there is provided a recording medium storing a program to be executed by a computer, the program including simulating a resist film based on an observed optical image of a mask pattern of a photomask obtained by receiving in an exposure apparatus a light which passed through the photomask and on a parameter showing a resist characteristic; inferring a dimension of the resist pattern based on the simulation; and deciding an optimum exposure condition based the inferred dimension of the resist pattern.